The technical scope of the present invention is that of plasma torches and more particularly torches used to ignite the propellant charge of a piece of ammunition.
A plasma torch is a system that enables high pressure (around 500 MPa) and high temperature (over 10000 K) gases to be generated by a high voltage (around 20 kV) electrical discharge made between two electrodes.
Plasma torches are used in industry, for example, to cut conductive materials, or else to destroy certain products or materials, or to carry out metallic deposits. They are also used in the field of armaments to generate pressure allowing a projectile to be fired.
Known plasma torches comprise an anode and a cathode separated by a capillary tube made of a material that is both electrically insulating and able to decompose in order to generate a plasma (for example a plastic material). The electrical discharge between anode and cathode is excited by means of a copper fuse or other conductive material. The electric arc thus created produces a plasma, which ablates the capillary tube wall, thereby causing the generation of light high pressure high temperature gases.
These gases are used either to directly accelerate a projectile, or to vaporise a working fluid (for example, water) allowing the volume of the gas to be increased.
Patents FR2754969 and FR2768810, which describe plasma torches used to ignite the propellant charge of a piece of ammunition, may be consulted.
One drawback to known plasma torches lies in the fragility of the fuse wire allowing the plasma to be excited. Such a fuse wire has a diameter of 0.1 to 0.5 mm. It may break further to thermal and mechanical stresses (vibration, impacts) that occur during the storage and implementation phases of the ammunition elements.
Moreover, the manufacture of known torches is made difficult and costly by the operation to mount such a fuse.
A plasma torch is also known by U.S. Pat. No. 5,503,081 that incorporates a fuse made in the shape of a tube of porous aluminium. It may also enclose an energetic fluid that is dispersed with the plasma through the propellant charge.
This fuse takes up a lot of space and requires a certain energy level to vaporise and ignite a plasma arc. This results in difficulties in integrating such a torch in a combat vehicle where electrical energy resources are obligatorily reduced. The aim of the invention is to overcome such drawbacks.
Thus, the torch according to the invention has improved mechanical strength thereby improving its reliability. Moreover, it is simple in structure and may be manufactured at a low cost.
Furthermore, the torch according to the invention incorporates a fuse of reduced mass requiring a reduced level of energy to be vaporised. According to the invention, this fuse associates at least one conductive material and at least one energetic or reactive material, that is to say one able to react with the conductive material.
These materials are associated:
either in the form of a homogeneous mixture of pulverulent materials, agglomerated with the possible addition of a binder,
or in the form of the close contact of at least one layer of conductive material with at least one layer of energetic or reactive material.
These two embodiments of the invention share the common characteristic of closely associating a relatively reduced mass of conductive material that is vaporised from the onset of the application of the serviceable voltage and causes either the ignition of an energetic material or the chemical reaction of a reactive material with the conductive material.
In any event, the chemical energy released by the reaction thus provoked is produced in the form of a combustion flame that will act as a conductive medium ensuring the passage of the electric arc of the plasma.
In the torch known by U.S. Pat. No. 5,503,081 a porous metallic fuse is firstly vaporised to ensure the ignition of the electric arc then releases a combustible or energetic material that will be spread by the plasma. The vaporisation of this porous metallic fuse as well as the dispersion of the material it encloses will consume energy and therefore reduce the temperature of the plasma generated, thereby reducing the igniting performance.
On the contrary, in the torch according to the invention, the total mass of the fuse implemented is very reduced (around a few hundreds of milligrams). It therefore consumes little energy but is enough to ignite the energetic material or trigger the reaction of a suitable reactive material with the conductive material.
The flame thus produced is a conductive medium that allows the arc between the electrodes and the torch to be maintained using a minimum serviceable voltage (around 1000 volts for an air gap of 10 cm, whereas known torches operate at between 10 KV and 30 KV for an air gap of 10 cm).
Such functioning cannot be obtained, however, using the structure of the porous fuse described by U.S. Pat. No. 5,503,081. Indeed, the porosity of the tube is difficult to control. Consequently, the relative proportions between conductive and reactive materials are fixed by the porosity and may therefore not be adjusted so as to ensure a chemical reaction between these two materials. Moreover, a porous metallic tube such as that described by U.S. Pat. No. 5,503,081 cannot accommodate a solid reactive or energetic material such as a pyrotechnic composition in its pores.
The torch according to the invention can be made without any difficulty at very different lengths.
A further subject of the invention is an igniter squib tube for an ammunition that incorporates such a plasma torch.
Thus, the invention relates to a plasma torch comprising at least two electrodes separated by a cylindrical insulating case delimiting an internal volume, said electrodes connected by a conductive ignition fuse placed in the internal volume, said torch wherein the fuse comprises at least one conductive material associated with at least one energetic material or one able to react with the conductive material.
The conductive material will be constituted by carbon or else a metal.
The energetic material or material able to react with the conductive material may be selected from among the following compounds or compositions:
Copper oxide; polytetrafluoroethylene; chlorofluoroethylene copolymer; polytetrafluoroethylene/chlorofluoroethylene copolymer; Magnesium/polytetrafluoroethylene/chlorofluoroethylene copolymer; Boron/potassium Nitrate; plasticised nitrocellulose coating or film; polyvinyl nitrate; Polyoxymethylene; polychlorotrifluoroethylene; polyvinyl chloride; polychlorotrifluoroethylene; polysulfone; polyvinylidene fluoride.
According to a first embodiment of the invention, the conductive material can be in the form of a powder or of particles mixed with the energetic material or with the material able to react with the conductive material.
The fuse may thus be made of a homogeneous mixture associating 6 to 40% in mass of conductive material powder and 60 to 94% in mass of an energetic material or one able to react with the conductive material.
The fuse can thus be made of a homogeneous mixture associating:
10 to 40% in mass of copper powder, and preferably 20%,
60 to 90% in mass of a composition associating Magnesium, polytetrafluoroethylene and chlorofluoroethylene copolymer, and preferably 80%.
The fuse can also by made of a homogeneous mixture associating:
10 to 40% in mass of silver powder, and preferably 20%,
60 to 90% in mass of a composition associating Magnesium, polytetrafluoroethylene and chlorofluoroethylene copolymer, and preferably 80%.
The fuse can also be made of a homogeneous mixture associating:
10 to 40% in mass of silver powder, and preferably 20%,
60 to 90% in mass of a composition associating Boron and potassium nitrate, and preferably 80%.
According to a second embodiment, the conductive material may form at least one layer deposited over at least part of the energetic material or material able to react with the conductive material.
The fuse may thus comprise at least one conductive layer of aluminium or magnesium deposited on a reactive layer of polytetrafluoroethylene, or nitrocellulose or polyvinyl nitrate, or copper oxide or chlorofluoroethylene copolymer, or polyoxymethylene, or polychlorotrifluoroethylene, or polysulfone, or polyvinylidene fluoride.
The dimensions of the different layers will be selected such that 85 to 95 parts in mass of the conductive layer material will be associated with 5 to 15 parts in mass of the material or material of the reactive layer or layers.
The fuse may comprise at least one layer of aluminium and at least one layer of chlorofluoroethylene copolymer.
Advantageously, the fuse may also comprise at least one layer of flame intensifying material.
The flame intensifying material may be polyoxymethylene or nitrocellulose.
The mass of the flame intensifying material may represent between 15 and 25 parts in mass added to the other materials of the fuse.
The fuse may advantageously be in the shape of a tube placed in the internal volume.
The tube may have at least one longitudinal slit.
The cylindrical insulating case may be placed in a tubular conductive body electrically connected to an electrode, the tubular conductive body being coated on at least part of its surface by an insulating material.
According to a variant embodiment, the tubular body may be perforated by at least two radial vents placed opposite radial holes made in the insulating case, vents and holes being obturated by the tubular fuse.
According to another variant embodiment, the front electrode may be perforated by an axial hole.
A further subject of the invention is an igniter squib tube for an ammunition comprising at least such a plasma torch.